1. Field of the Invention
This invention relates generally to carriage systems for heavy vehicles, and, more specifically, to track modules for use in connection with articulated steering tracked vehicles, the track module having a novel stabilizing mechanism to manage large torsional and horizontal forces induced upon the track module frame. In one aspect, the present invention provides an improved carriage assembly for an "articulated vibrator" vehicle used for generating acoustic energy for seismic exploration systems.
2. Background
Vehicles having a substantially rigid main frame supported and moved by two long track assemblies, one disposed along each opposing side of the frame, have heretofore been used as off-road vehicles for traveling over rough terrain. While the development of such vehicles has been the subject of inventive work and research, the prior art vehicles have not found wide acceptance for use as seismic vibrator vehicles for several reasons. Conventional tracked vehicles are generally very slow of speed and, therefore, difficult to move over long distances. These dual-track vehicles commonly use steel grouser bars in the tracks which cause damage to hard-surfaced roads, thereby limiting the vehicle to off-road operation only. Moreover, vehicles with long dual tracks "pitch over" upon the cresting of a hill or rise. The shock due to pitching makes the operation of the vehicle relatively uncomfortable for the driver-operator and can result in damage, not only to the vehicle itself, but also to the expensive seismic exploration apparatus mounted on the vehicle. Because of the remoteness of the areas in which seismic exploration vehicles are employed, breakdowns are extremely costly. Because of these problems, rigid frame dual track seismic exploration vehicles are not favored in the industry.
Yet a tracked vehicle, if it did not possess the aforementioned disadvantages, would clearly rate above seismic exploration vehicles having a tire and wheel carriage system. Because the gross weight of a typical seismic vibrator is about 65,000 pounds, supported on four tires each having a footprint of about 620 in..sup.2, the ground pressure under each footprint averages around 26 psi and peaks at the tire center at around 40 psi (the typical pressure of the tire). When operating in sand hills, such as in the deep desert where blown sand may pile up to 1000 feet high, vehicles having a tire and wheel under-carriage system are prone to bury, especially when attempting to traverse a grade. Consequently, heavy seismic vibrator vehicles with excessive ground pressure (&gt;10 psi) cannot negotiate many sand mountains where they need to go. The heavy footprint of these vehicles is also a disadvantage in deep snow and delicate tundra encountered in arctic regions. A track-type under-carriage system would have a much lighter footprint and would be able to more easily navigate rough terrain without damaging the environment. Also, because tracked vehicles do not utilize pneumatic tires, no "down-time" would be encountered due to flat tires.
Thus, a need exists for a new and improved modular carriage system, especially of the articulated steering 4-track type, for seismic vibrator vehicles. For obvious reasons, it also would be beneficial for the modular carriage system to be capable of retro-fit onto existing seismic vibrator vehicles having only two axles.
After-market retro-fit modular track-type carriage systems for vehicles in general are known. Existing configurations fall into two basic categories. The most common type is the "triangular track configuration" which uses an elevated, relatively small diameter drive wheel. This triangular-shaped track module attaches to one end of a single driving axle. The second type uses a large diameter drive wheel which clones the radius of the original tire and wheel assembly. This second type track module has the advantage of using the same axle ratio as the original tire-equipped unit, and, therefore, retains the speed and gradability of the original machine. This assembly also attaches to one end of a single driving axle on a vehicle with an articulated frame.
Existing single axle track carriage systems, however, are not capable of handling the heavy loading and high axle torque generated by large vehicles, such as heavy seismic vibrator vehicles. Such heavy vehicles with modular track carriage systems also generate high torsional and horizontal (lateral) loads which are incapable of being managed by existing track module geometries. In addition, if a track module carriage system is to be used in a large, off-road vehicle, such as a seismic vibrator, the track module should have the capability to vertically oscillate so that the full footprint of the track remains in contact with the ground, even over very rough terrain. Present systems lack this high oscillating capability.
Thus, for a 4-track carriage system to be successfully implemented in the field of heavy vehicles it must possess a structural geometry to withstand heavy loading and high axle torque and include a mechanism to control the large torsional and horizontal dynamic loads induced onto the track module frame. To function as a seismic exploration vehicle it must also be smooth running (at speeds up to 20 miles per hour) and capable of navigating hills and obstacles without significant pitching. A system achieving these objectives would be a valuable advancement in heavy, off-road vehicle design.